With respect to one example of well-known air conditioners, there has conventionally been a type in which a refrigerant circulation circuit is formed by a circulation circuit running through a condenser, a pressure reducing device (expansion valve), an evaporator, and a variable displacement compressor (particularly a suction chamber, a cylinder bore, and a discharge chamber on the inside thereof). In those air conditioners, there is known a type in which a control valve in the variable displacement compressor has a function of detecting, as an index for estimating the refrigerant discharge capacity, a differential pressure between two pressure monitor points set in the refrigerant circulation circuit, and performing a feedback control of the discharge capacity of the variable displacement compressor so that the differential pressure between the two points approaches a set differential pressure, and further, a controller disposed outside the refrigerant circulation circuit determines or recalculates the set differential pressure based on switching information from a mode selector switch and an airflow switch of an air-conditioning operation panel (which is used as information for notifying a sudden change in cooling load to the controller in advance or simultaneously with the change) and commands the control valve to change the set differential pressure, and hence, having such a functional structure makes it possible, in addition to enabling both a discharge capacity control of the compressor for stable maintenance of a room temperature and an emergent temporary quick change in discharge capacity, to improve an accuracy and a response characteristic of the control for the stable maintenance of the room temperature.
Such an air conditioner is disclosed in, for example, Japanese Patent Application Publication (JP-A) No. 2001-140767.
On the other hand, in case of this air conditioner, the differential pressure caused by the refrigerant flow between the two pressure monitor points is detected by a differential pressure sensor for detecting the refrigerant circulation amount in the refrigerant circulation circuit, and the feedback control of the discharge capacity in the variable displacement compressor is carried out by observing correlation between the differential pressure between the two pressure monitor points obtained herein and the refrigerant circulation amount. However, it is essential to accurately detect the differential pressure in order to stably carry out the feedback control of the discharge capacity herein.
In view of this, it is effective to apply a technique of lengthening a distance between the two pressure monitor points or providing a restriction member in the refrigerant circulation circuit in order to improve the accuracy of the detection of the differential pressure between the two pressure monitor points. However, there is a problem that when such a structure is adopted, the basic structure of the air conditioner becomes complicated or the design of the variable displacement compressor becomes complicated, and therefore, it is actually difficult to apply it and, as a result, the basic performance is not fully exhibited.
Specifically, when there is applied the structure in which the distance between the two pressure monitor points is lengthened, one (a conduit from a pressure monitor point P1 in case of FIG. 1) of two conduits joined to a main pipe, where a refrigerant flows, for leading the refrigerant from its pressure monitor points P1 and P2 to a differential pressure sensor 100 should be made long as shown in FIG. 1. As a result, the basic structure of the air conditioner becomes complicated.
On the other hand, when there is applied the structure in which the restriction member is provided in the refrigerant circulation circuit, a restriction member 101 is provided between pressure monitor points P1 and P2 in a main pipe where a refrigerant flows and it is possible to make short two conduits joined to the main pipe for leading the refrigerant from its pressure monitor points P1 and P2 to a differential pressure sensor 100 as shown in FIG. 2. However, in case of this structure, the efficiency of the air conditioner is lowered due to occurrence of a pressure loss caused by the restriction member 101 and, as a result, the design of the variable displacement compressor becomes complicated. In particular, when the differential pressure between the two pressure monitor points P1 and P2 is directly used as a force against an electromagnetic force of the control valve of the variable displacement compressor, a passage is required for leading the pressure at one of the two pressure monitor points P1 and P2 to the variable displacement compressor, while, when the restriction member 101 is disposed inside the variable displacement compressor and the differential pressure is used as a force against an electromagnetic force of the control valve, the problem of pressure loss cannot be avoided and further a differential pressure passage should be provided inside the variable displacement compressor. Consequently, in any event, the design for improvement of the variable displacement compressor becomes complicated.
It is therefore a technical object of the present invention to provide an air conditioner that can easily perform detection of a refrigerant circulation amount accurately and properly with a simple structure and that can further improve a basic function including an accuracy and a response characteristic of a control for achieving stable maintenance of a room temperature.